Flexible tie strut

ABSTRACT

A flexible tie strut for supporting both compressive and tensile forces, the flexible tie strut includes a tension member and a coaxially mounted compression member, the compression member and the tensile member are interconnected at their respective ends. A coupler for interconnecting flexible tie struts, and a system of couplers and struts are also disclosed. Additionally, wheels are disclosed that have axles having both male and female connection means.

This is a continuation-in-part application of U.S. patent applicationSer. No. 08/118,492, filed Sep. 7, 1993, now U.S. Pat. No. 5,433,549,issued Jul. 18, 1995.

FIELD OF THE INVENTION

The present invention is directed to a construction system, especiallyuseful as a construction toy, display stand, instructional engineeringaid and more particularly to a novel and improved type of flexible tiestrut. The present invention also relates to couplers for connectingstructural members and collapsible, self-erecting constructionstructures.

PRIOR ART

The range of construction toys available today for children older thansix years is small and generally unappealing. There are two majorproblems associated with this section of the toy market. First, theshort attention span of many of today's television-oriented childrenrequires a toy to provide immediate gratification--the `push-together`ease of the Lego™ is now a minimum standard. Second, there isconsiderable buyer resistance to construction toys which manifestly donot contain sufficient components to build the impressive models sooften seen in shop-window displays and advertising literature and whenthey do, they are fragile not durable.

Although examples of toys are discussed in detail it is understood thatthe present invention is directed to construction systems in which theprimary types of structural members are beams, ties and struts. Beamsare those members that are subjected to bending or flexure. Ties aremembers that are subjected to axial tension only. Struts are membersthat are subjected to axial compression only. The present invention isable to support tension and compression loads and in addition, isflexible and collapsible. After being collapsed and bent, the flexibletie strut is able to elastically recover to it's original form.

A variety of construction toys having combinations of connectors andstructural elements acting primarily as struts which can be combined toform various structures is generally known. The structural elements ofthe known construction toys generally do not accommodate tensile loadsor allow recoverable bending along their longitudinal axis. Such knownelements seriously limit the size and strength of structures that can beassembled from them.

If a large structure is fabricated from existing combinations ofconnectors and structural elements, such a structure can easily bedamaged from the application of small loads. The reason for this is, theapplication of a relatively small load can cause significant bendingstress to be developed in the struts, thus damaging them. The presentinvention is designed to support only compressive and tensile loads andcannot support excessive bending loads. This feature of not beingcapable of supporting excessive bending loads not only prevents damagein the event of overload of the structure, but also permits thestructure to be collapsed and stored for later self-erection.

U.S. Pat. Nos. 5,137,486 to Glickman and 2,709,318 to Benjamin aretypical of construction toys having hub-like connectors and strut-likestructural elements adapted to be removably engaged, e.g., force fit,with the connectors to form composite structures. In general, none ofthese prior art devices provides positive coupling of strut-like membersto withstand tensile loading, and none provides strut-like members withstrength in tension and compression. In addition, none of the strut-likemembers in the prior art allows controlled flexure for purposes ofassembly or the creation of self-erecting structures.

In U.S. Pat. No. 2,976,968 to Fentiman, an attempt is made at producinga construction system which is able to load the strut members in tensionand compression, but this design is susceptible to damage due to therigid nature of both the struts and the coupler.

In U.S. Pat. No. 4,302,900 to Rayner and also U.S. Pat. No. 3,286,391 toMengeringhausen, a flexible connection means is disclosed. Thisconnection means is able to accommodate a certain amount of abuse, butbecause the strum in both of the aforementioned patents are rigid, theyare easily damaged if subjected to bending loads as might occur if theywere to be stepped on. The present invention cannot be damaged in thisway since it cannot support excessive bending loads, and thus cannot bedamaged by them.

Because of the limitations of existing construction systems thefollowing criteria were considered in the design of the subjectinvention:

Maximum versatility of each pan (as discussed above) to provide thelargest possible variety of structures is desirable

No tools are required for assembly

Rapid assembly and disassembly are desirable

Engineering principles are illustrated as graphically in this inventionas bricklaying systems can be illustrated with block systems

Random or violent disassembly must not damage the parts

Tenacity of connections must not be dependent on close toleranceinterference fits which may be affected by wear

Parts must be large enough to not be easily lost

Sharp edges and corners must be eliminated to prevent soreness tofingertips after an extended period of use

Completed structure must be collapsible and capable of re-erection

In view of the limitations of prior art devices and, in general, themany primary types of structural elements required to build structures,it would be highly desirable to have one building element that would beselectively flexible (even recoverable) and have sufficient strength intension and compression in order to build any size structure. It wouldalso be desirable to have a unique coupler for positively locking withsuch a novel building element.

SUMMARY OF THE INVENTION

The purpose of the subject invention is to provide a construction systemhaving elements which are flexible and recoverable along theirlongitudinal axis and which support tensile and compressive loads. Toaccomplish this purpose there is provided a construction system having aunique building element which is a flexible tie strut (hereinafter alsoreferred to as "FTS") comprising a tension member and a co-axialcompression member, the members being connected to each other at theirrespective ends. The tension member is preferably a flexible cable-likemember which provides resistance to tensile forces that may be appliedalong the longitudinal axis of the FTS. The compression member is aone-piece or multiple-piece elongated member which is flexible about itslongitudinal axis and which is substantially incompressible along itslongitudinal axis when subjected to axial compression. The compressionmember is preferably a helical spring, the coils of which allow flexingof the spring but which contact each other and become incompressiblewhen the spring is fully loaded. The novel combination of the tensionmember and compression member being connected to each other at theirrespective ends allows the FTS to bend along its length, to return to astraightened shape upon release of bending forces and to withstandtension and compression. In addition, the FTS may be designed to buckleat a predetermined compressive load by either varying the diameter orlength of the compressive member or the initial preload on the tensionmember. In addition, the tension and compression member may be preloadedagainst each other to increase the stiffness of the FTS.

In one aspect of the invention is a flexible tie strut for supportingboth compressive and tensile forces having a tension member beinggenerally elongated, flexible along the length thereof and having firstand second ends, said tension member providing resistance to tensileforces that may be applied to said first and second ends; and acompression member being generally elongated, flexible along the lengththereof and having first and second ends, said compression member havinga substantial portion thereof which is incompressible, said compressionmember providing resistance to compressive forces that may be applied tosaid first and second ends, said first end of said tension member beingoperatively connected to said first end of said compression member andsaid second end of said tension member being operatively connected tosaid second end of said compression member, at least one of said membershaving some compliance to allow flexibility of the flexible tie shut.

In another aspect of the invention there is provided a coupler having abody of two identical pieces, each piece having a perimeter and havingan axis therethrough and being generally symmetrical about said axis,each piece having a portion of at least one cavity in the perimeterthereof, said pieces being connected together in mirror image fashion toform said body having cavities in the periphery thereof to form atwo-dimensional connector.

In still another aspect of the invention there is provided a couplerhaving a body having a perimeter and at least one cavity, in saidperimeter, said cavity having at least one tooth extending into saidcavity to engage a connector means of a tie strut to be mated to saidcoupler.

In yet again another aspect of the invention there is provided aconstruction system having a flexible tie shut for supporting bothcompressive and tensile forces having a tension member being generallyelongated, flexible along the length thereof and having first and secondends, said tension member providing resistance to tensile forces thatmay be applied to said first and second ends and a compression memberbeing generally elongated, flexible along the length thereof and havingfirst and second ends, said compression member having a substantialportion thereof which is incompressible, said compression memberproviding resistance to compressive forces that may be applied to saidfirst and second ends, said first end of said tension member beingoperatively connected to said first end of said compression member andsaid second end of said tension member being operatively connected tosaid second end of said compression member, at least one of said membershaving some compliance to allow flexibility of the flexible tie strut;and a coupler for connecting struts, the coupler having a member havingat least one opening for receiving a strut to be connected therein and aretaining means connected to said member and positioned within saidopening for locking engagement with a strut to be connected.

In yet another aspect of the invention there is provided a self-erectingsystem comprising a flexible tie strut for supporting both compressiveand tensile forces having a first connector means attached to the firstends of said tension member and said compression member and a secondconnector means attached to said second ends of said tension member andcompression member to connect said flexible tie strut to objects to beconnected and having a coupler having a body of two-identical pieces,each piece having a perimeter and having an axis therethrough and beinggenerally symmetrical about said axis, each piece having a portion of atleast one cavity in the perimeter thereof, said pieces being connectedtogether in mirror image fashion to form said body having cavities inthe periphery thereof to form a two-dimensional connector.

In still yet another aspect of the invention there is provided a selferecting system comprising a flexible tie strut wherein said connectormeans includes at least a portion of a circumferential resilient rib,said rib being deflected upon mating of said strut to said coupler.

In another aspect of the invention there is provided wheel assemblyhaving a wheel assembly having at least one wheel having a rotationalaxis and having an opening therethrough concentric with said axis; andan axle-like member insertable within said opening, said axle likemember having a connector means that is integral with each end thereof,said connector means being a quarter-turn connector at one end and acavity having at least one tooth at the other end thereof.

DESCRIPTION OF THE DRAWING

FIGS. 1A and 1B are partial cross-sectioned plan views of a FTS with apair of connector means at each end thereof. Flexure of the FTS is shownin FIG. 1B.

FIG. 2A is an enlarged cross-sectional view of one end of the FTS shownin FIG. 1A.

FIG. 2B is an enlarged cross-sectional view as in FIG. 2A of the end ofthe FTS as shown in FIG. 1B. An alternate embodiment of tensile memberhaving a leader portion shown in phantom line is illustrated.

FIG. 3A is an enlarged view of an end portion of another embodiment of aFTS having alternate adjustable tension means and alternate connectormeans.

FIGS. 3B and 3C are enlarged views of a section of the FTS withalternate embodiments of compression members. In FIG. 3B, thecompression member is a plurality of flat discs. In FIG. 3C, thecompression member is a plurality of fitted (shown curved) discs.

FIG. 4 is an enlarged view similar to FIG. 3A of another alternateembodiment of connector means having a jam nut to controlcompressibility and flexure of the FTS.

FIGS. 5A and 5B are perspective views of half of a two-dimension couplerand an assembled two-dimensional coupler, respectively in accordancewith the invention. FIG. 5B illustrates two identical coupler halves asseen in FIG. 5A bonded together.

FIG. 6A and 6B are perspective views of a three-dimensional coupler.FIG. 6A illustrates in exploded view two two-dimensional couplers asshown in FIG. 5B prior to interlocking to each other. FIG. 6B is anassembled three-dimensional coupler after interlocking of the two,two-dimensional couplers of FIG. 6A.

FIG. 7 is an enlarged perspective view of one end of the connector meansof the FTS shown in FIG. 1A.

FIG. 8 is a partial cross-sectioned plan view similar to FIG. 1A of aFTS mated at each end thereof to two-dimensional couplers as seen inFIG. 5B.

FIG. 9 is a perspective view of a self-erecting structure of multipleFTS and alternate embodiments of three-dimensional couplers inaccordance with the invention.

FIG. 10A is a graph of Force versus Angular Deflection of a FTS and of asimple spring when loaded as a single cantilever beam. FIG. 10B is agraph of force versus deflection of an FTS and of a simple spring whenloaded in column.

FIG. 11A is a cross-sectional view of a portion of an FTS springcompression member bent into a 0.500 inch bend radius.

FIG. 11B is a cross-sectional view similar to FIG. 11A of a portion of asimple spring having the same preload as the FTS compression membershown in FIG. 11A and bent into the same 0.500 inch bend radius as theFTS in FIG. 11A.

FIG. 12A illustrates in end view a wheel assembly and axle-like memberwith integral connection means. FIG. 12B illustrates in cross sectionview the wheel, axle and connection means shown in FIG. 12A.

FIG. 13 illustrates a mated tandem pair of the wheel assembly, axle andthe axle-like members shown in FIGS. 12A and 12B.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With continued reference to the drawing, FIGS. 1A and 1B illustrate thecomposite struts in accordance with the invention. Each assemblyincludes the FTS shown generally at 1 comprising tension member 3 andcompression member 5. Tension member 3 and compression member 5 areoperatively connected to each other at their respective ends by a pairof connector means 7 which also mates the FTS to objects to beconnected. FIG. 1B illustrates the flexibility of the FTS.

Tension member 3 has a first end 11 and second end 13. Compressionmember 5 has a first end 15 and a second end 17. The first end 11 of thetension member is operatively interconnected to the first end 15 of thecompression member 5, and the second end 13 of the tension member 3 isoperatively interconnected with the second end 17 of the compressionmember 5. The cross-sectioned portions of FIGS. 1A and 1B illustrateoperative interconnection of ends 11 and 13 of tension member 3 and ends15 and 17 of compression member 5 by compliant sections 18 ofcompression member 5. One or both compliant (compressible) sections 18of compression member 5 may be used to allow a greater range offlexibility of compression member 5. In FIG. 1B, the allowablecompressibility of compliant sections 18 have been utilized by theflexure of the FTS.

As can be seen more clearly in FIG. 2A, tension member 3 is shown to bea cable-like member, the ends of the cable-like member being preferablybarbed at 20 to operatively engage collar 9 of connector means 7. Asshown in FIGS. 1-4, knob means 25 can be integral or a part of connectormeans 7. Connector means 7 further includes end portion 23 for lockingan assembled FTS to objects to be connected, as will be discussed laterin greater detail. Connector means 7 also includes an integral knobportion 25 which allows manipulation and especially rotation of endportion 23 for purposes of coupling and locking assembled strut 1 to anobject to be connected. It is understood that the ends of the tensionmember 3 and the compression member 5 may be operatively interconnectedto support tensile and compression loads by equivalent means, such ascrimping, soldering, welding, adhesives, etc., well known to one skilledin the art and are considered part of this invention. The connectormeans may be injection molded onto the first and second ends of thetension means.

Flexibility of FTS depends upon either the compressibility ofcompression member 5 or the elasticity of tension member 3, or both.Compression member 5 is shown to be a helical spring-like member havingcoils which when fully compressed, i.e., when contacting each other,become the equivalent of a tube. The cross-section of such coils may beround, square, rectangular, etc. and may be segmented to vary along theaxial length of the spring. If a external load compresses all of thecoils of compression member 5 into contact with each other, as seen inFIG. 2B, then the FTS will become resistant to both tensile andcompressive forces when used as a structural member. Various mechanismsto selectively apply tension to tension member 3 with respect tocompressive member 5 are within the scope of the invention. By varyingthe preload between the tension and compression members the stiffness ofthe FTS can be tailored to a specific valve. FIGS. 1A-B, 2A-B, 3A and 4illustrate alternative embodiments to adjust or control the interactionbetween tension member 3 and compression member 5. FIGS. 10A and 10Billustrate the effect of the additional stiffness of a FTS type ofconstruction versus a simple spring. The simple spring does notincorporate a tensile member, thus cannot support significant tensionloads or be preloaded to adjust it's stiffness.

The bending stiffness of a plain extension spring is determined by theamount of initial preload that can be wound into the spring duringfabrication. This mount of preload is determined by the spring materialproperties, the spring dimensions and the spring winding parameters.Simply, as the spring is wound the coil being added is wound partiallybehind the existing coil. The extent that this can be accomplishedwithout having the added coil on top of the existing coils determinesthe mount of preload due to winding parameters. As example a 1/4 inchoutside diameter spring made from 0.032 diameter hard drawn steel wirehas a practical maximum initial preload of 1 pound. In other words at aload of 1 pound in tension the coils of the spring would just begin toseparate. Thus a spring such as this, subject to a bending load wouldremain straight until this 1 pound limit between coils was reached andit's coils separated thus deflecting it.

The stiffness of the FTS utilizing a coilbound spring as the compressionmember is determined by the initial tension that is wound into thespring and the additional stiffness that may be added by preloading thecompression and tensile members. For example if we take the same 1/4inch spring of the previous example and incorporate thecompliant/preload section of the present invention, the allowable loadwould be much greater. For example the compression spring section of FTSmade from the same 0.032 diameter wire, 1/4 inch outside diameter, cansupport a maximum load of 10 pounds before it will yield due totorsional stresses developed in the wire. Thus if this 10 pounds offorce is utilized to preload the coil bound portion of the FTS, it willnow take; 10+1=11 pounds of force to separate the spring coils causingit to bend. This stiffness increase is achieved without sacrificing anyflexibility since the spring configuration did not change. If a plainextension spring were designed to have same 11 pounds of initial tensionin a 0.250" diameter spring, the wire diameter would have to beincreased to 0.065" in diameter. A spring with this 0.065" wire diameterand 11 pound preload has one tenth the elongation range of the original0.032" wire thus it would yield during bending and not elasticallyrecover. In addition to the limited elongation range due to hightorsional stresses wound into the wire the simple spring with it's 0.065diameter wire has a fewer number of active coils in bending as shown inFIG. 11A and 11B.

The allowable deflection of a tightly coiled spring in bending is afunction of the number of active coils involved in the bend, the amountof initial preload wound into the coil and the torsional stressdeveloped during the bending. The amount of torsional stress developedis dependent among other things, the wire diameter used to wind thecoil. If a large amount of torsion stress due to bending is encounteredas would be the case with a 90 degree bend as shown in FIGS. 11A and 11Ba small wire diameter would provide the lowest torsional stress and thegreatest number of active coils to distribute that stress. Comparing aFTS with 11 lbs of preload versus a simple spring also with 11 lbs ofpreload;

FTS

Initial preload=11 lbs.

Spring diameter (Dimension A): 0.25"

Wire diameter (Dimension B) 0.032"

Number or coils per inch=1/0.032=31

angular deflection (Angle C) between coils on 0.500" dia bend radius(Dimension D)=3.1 degrees

Spring

Initial preload=11 lbs

Spring diameter (Dimension E): 0.25"

Wire diameter (Dimension F) 0.065"

Number of coils per inch=1 /0.065=15

angular deflection (Angle G) between coils on 0.500" dia bend radius(Dimension H)=7.2 degrees

With a high initial preload the amount of initial torsional stress isalso high in the simple spring. Due to this high initial torsionalstress there is little additional torsional stress that can beaccommodated due to bending. This severely limits the amount of bendingthat can be accommodated without permanently deforming the spring. Toadd to this drawback is the fact that the individual coils mustexperience a greater angular deflection for a given bend radius andstrut diameter as shown in FIGS. 11A and 11B. As shown in FIG. 11B the0.065 wire diameter spring is subjected to more than twice the angulardeflection per coil versus the 0.032. This additional angular deflectionon top of a already high torsional stress severely limits the amount ofelastic bending allowable. The simple spring shown in FIG. 11B wouldyield after being bent in the 0.500" bend radius shown and not be ableto recover straight. The FTS on the other hand has a small amount ofbuilt in torsional stress, or none at all in the case of segmenteddisks, and thus has a large elastic range in bending. The addedstiffness of a FTS promotes a very stiff structure when it is used ineither a straight or a curved configuration yet provides the maximumelongation necessary for curved fabrication and collapse andre-erection. In addition the resistance to buckling is greatly enhancedwith the additional preload because this high initial preload causes theFTS to remain very straight prior to the application of a compressiveload.

When the FTS is bent a additional unique feature is exhibited. This isshown in FIG. 10. With the application of a perpendicular load, the FTSresists the load by a combination of the inherent initial preload woundinto the spring and the preset preload present in the compliantsections. As the load is increased the FTS bends and in doing socompresses the compliant sections. With increasing deflection theresisting force of the FTS increases until the inner tensile membermoves from the center of the assembly to the side. When this occurs thepath length that the tensile member is forced to take is reduced and thedeflection of the compliant sections is reduced, thus reducing thepreload. This gives the FTS a over-center action latching action that isvery useful during the collapse of a FTS structure and is also usefulfor spring biased, resetable devices such as circuit breakers etc. Asshown in FIG. 10A, it takes a greater amount of force to cause the FTSto bend from a straight condition than to continue to bend it once thispeak is reached. This latching/detent action promotes rapid and rigidself-erection of structures made with FTS elements. The amount of detentaction and the change in slope of the force versus deflection curve isdictated by the change in path length the tensile member experiences asthe FTS is bent. If the change in path length is small as would be thecase in a small diameter, long spring, the detent action and slopechange would be very small. If, on the other hand the spring has a largeinner diameter and a short length, the path length change would be largeand so would the detent action and change the in slope of the forceversus deflection curve. This detent action is shown in FIG. 10A. Theportion or the curve labeled A shows the initial stiffness of the FTSand at point B the trip point, (detent), is reached. Continueddeflection after point B occurs with a negative spring rate. At point Dthe FTS once again behaves with a positive spring rate and it can beseen that it is nearly the same slope as a simple extension spring butat a higher preload. When a FTS is loaded in column as shown in FIG. 10the force versus deflection curve is similar to that in 10A, but thetrip point at B is much more pronounced and the portion of the curve atD is nearly flat. This high initial resistance to bending and subsequentvery flat spring rate, (force versus deflection curve) is also ideal forhuman powered devices such as exercise equipment and archery equipment,since the resistance of the developed load can be tailored to theapplication and the resisting force can be made nearly constant across alarge deflection range shown at E in FIG. 10B. In a archery bowapplication the behavior of the FTS in bending is similar to thatobtained from "compound" bows constructed using pulleys and cablesattached at various points along the bow. The FTS exhibits this highpositive spring rate, negative rate and then flat or positive ratewhenever it is bent regardless of the direction of the applied load. Inother words the FTS will exhibit this detent action if it is loadedperpendicular to it's length as shown in FIG. 10A or along its length asa column in compression as shown in FIG. 10B or even as a simple beamloaded in the middle and supported at both ends. During collapse of aFTS structure all of these various bending modes may be encountered. Ascan be seen in FIG. 10A and 10B the exact shape of the force versusdeflection curve and the forces obtained is adjustable by varying thepreload on the tension and compression members. The areas above thesimple spring curve in FIGS. 10A and 10B represent the possibleadjustment ranges for a FTS.

Since the total amount of compliance required to allow a FTS element tobend is relatively small, super elastic materials such as nickeltitanium shape memory alloys may be used for the tensile member. Withthis configuration a complete coil bound outer member as shown in FIG.2B and FIG. 8 may be used without any compliant sections sincesufficient compliance is available in the super-elastic tensile member.This configuration is especially useful since super-elastic alloysposses a very flat (little increase in force with increasing deflection)force versus deflection curve thus this combination would also yield avery flat force versus deflection curve. If the tensile member iscomposed of a split hystersis shape memory alloy a FTS structure couldbe stored collapsed and when desired, heated to recover the alloy andpermanently lock the FTS in a straight position.

As mentioned before, it should be understood that the flexibilitycharacteristics of the FTS including its having coaxially mountedcompression and tension members are different and superior to theflexibility characteristics of say, for example, a tightly coiledelongated coil spring alone. A coil spring alone does not havesufficient stiffness to even support itself when held horizontally atone end. In contrast, the FTS will remain rigid and straight whensupported at one end--even in long lengths. It is understood that it iswell within the scope of the invention to reverse or eliminate thecoaxial relationship of the tension and compression members 3 and 5,respectively, by mechanical expedients well known to one skilled in theart. Specifically, the combination of the tension and compressionmembers 3 and 5, respectively, provides an overall structure when thecompression member 5 is a helical spring or like functioning member, asdescribed earlier, having some degree of compressibility that will snapback into column as compared to a spring member alone. This featureallows the unique strut of the invention to be used advantageously forself-erecting structures.

As seen in FIGS. 3B and 3C, compression member 5 may further comprise aplurality of incompressible members, shown generally at 6, such as beadsor plates which when aligned or stacked on top of one another provide anincompressible column. The incompressible members 6 may be planar 8 orfitted 10, as shown in FIGS. 3B and 3C. Such members need only be strongin compression; thus they may be solid or composite, e.g., platesconstructed of honeycomb sections.

For a FTS to function properly and be able to support significantcompression loads the compression member segments must be aligned on topof each other. In the case where the compression member is a coil boundspring the individual coils are inherently aligned and stacked on top ofeach other. In the case of segmented disks, another method should beprovided to proved this initial alignment. One such method is toincorporate a form fitting shape such as that shown in FIG. 3C. Anothermethod would be to provide alignment on the tensile member itself with aclose fitting disk. Yet another method would be to incorporate amagnetic alignment system by magnetizing the disks so that they align bytheir mutual attraction.

A variety of materials may be used for the compression member, amongthem are conventional spring materials such as music wire and hard drawnsteel. Plastic materials may also be used such as PET (polyethyleneterephthalate) which can be wound hot into a coil spring shape. Glassfiber reenforcement may be added to increase the flexural modulus andalso increase the strength. If a larger preload is desired thanobtainable with a plastic spring, a steel spring may be added in linewith the plastic coil compression section. This plastic and steelconstruction is also shown in FIG. 2A with the line 27 denoting theoptional transition from plastic to steel. Section 18 is steel andsection 5 being plastic. If a very lightweight FTS is desired, thecompression member may be composed of honeycomb material, which isextremely strong in compression yet very light weight. In general,compression member 5 may be fabricated from a variety of suitablematerials such as metals or polymers or combinations of materials whichwill provide the compressive resistance required of the invention. It isalso within the scope of the invention to fabricate the compressionmember 5 either structurally and/or with a choice of materials to varythe compressibility of compression member 5, e.g., combinations ofcompressible, variably compressible and/or incompressible members.

FIGS. 4 discloses mechanical means to control the compressibility ofcompression member 5. It is within the scope of the invention tofabricate compression member 5 of a material or materials which changein strength or dimension as desired. An example of such a material wouldbe a recoverable shape memory alloy, e.g., a nickel titanium shapememory alloy or heat-recoverable polymeric materials or the like. It isunderstood that shape memory alloys include those exhibitingpseudoelasticity, superelasticity or the like, or heat recoverability.

The strength of a structure constructed from the FTS ideally is limitedby the compressive load imposed upon an individual FTS. As the load on astructure is increased, the structure will remain stable until thecritical buckling load of an individual FTS is reached. When this occursthe structure will partially or fully collapse. The generic Eulerequation governs this buckling behavior. As known to one skilled in theart, buckling load, F_(cr) ##EQU1## where L is the strut length (in); Iis the section modulus (in⁴); E is elastic modulus (psi); and K is aconstant. For purposes of the subject invention, K equals 1. Since thestrut of the subject invention is a composite structure E must bemeasured experimentally.

As noted earlier with respect to the subject invention, by increasingthe diameter of the struts as their length increases it is possible toprovide a uniform buckling factor throughout the structure. As can beappreciated the FTS will not be damaged due to buckling because itcannot develop excessive bending stresses because of its construction.Removal of the load will allow the FTS to return to its straightenedshape. Likewise, a structure made of a plurality of FTS will self-erectwhen unloaded after being collapsed. This inherent characteristic of astructure constructed of FTS elements allows it to not only resistdamage, but also allows it to be collapsed and stored for laterself-erection.

As shown in FIGS. 1A and 1B, tension member 3 is preferably a cablewhich is flexible in bending along the length thereof but generallyfixed in length to support tensile loads. The term "cable" is understoodto include monofilament or multi filament for purposes of description.Tension member 3 may be a monofilament of polymeric or metallicmaterials or a multiple-strand cable of one or more materials asdesired. It is also within the scope of the invention to have tensionmember 3 made of materials which also change in strength and/ordimension as desired, for example, heat-recoverable shape memory alloysor heat-recoverable polymers. It is further within the scope of theinvention to make the tension member 3 from materials that exhibit ahigh degree of flexibility such as shape memory alloys of nickeltitanium and other materials which exhibit pseudo elasticity orsuperelasticity. Shape memory alloys and polymers are well known to oneskilled in the art, and the selection of appropriate materials fordesired loading and/or motion is considered to be within the scope ofthis invention. Since the flexibility of the FTS, as seen in FIGS. 1A-B,is dependent upon the degree of preloaded compression of the compressionmember 5 determined by the tension in tension member 3, it is within thescope of the invention to vary the materials and/or mechanicalinterconnection of these members to control the flexibility of the FTS.

FIG. 3A illustrates the end portion of an alternate embodiment of theFTS having tension member 3 and compression member 5. In thisembodiment, a spring 22 is interposed between tension member 3 andcompression member 5. Specifically, at one end, spring 22 contacts stop24 on tension member 3, and at the other end, spring 22 contacts crimpstop 26 which is in turn connected to compression member 5. Stop 24 isfree to move and compress spring 22 upon flexure of the FTS. A positivelimit to the amount of allowable elongation is reached when spring 22 isfully compressed.

A complete FTS assembly is shown in FIG. 1A. As seen in FIG. 2A thetensile member 3 has barbs 20 at each end. These barbs provide a snaptogether assembly of the connection means 7 and the tensile member. Thesequence of assembly is as follows: one connector means is slipped overleader portion 21 of tensile member 3 and either pushed or pulled intosnap fit collar section 9. The compression member 5 is slipped over thetension member 3 and the other connector means piece is slipped over theremaining free end of the tensile member 3. The assembly is completed bypulling on leader portion 21 until the preload/compliant sections 18 arepartially compressed and barb 20 snaps into collar 9. The protrudingleader portions 21 may be cut flush with the connector means afterassembly. As can be appreciated, leader portions 21 are not requiredwhen the entire assembly is pressed together by aligning all of thecomponents in line, in a fixture which prevents buckling of thecompression member, and a compressive force is then applied to both endsof the assembly and this compresses the compliant sections 18 and drivesbarbs 20 into their respective collars. This type of assembly ispossible if tensile 3 is not allowed to buckle under the assembly loadprior to both barbs snapping into their collars.

In FIGS. 3A and 4 connector means 7 is shown to be a well-known quarterturn fastener. This fastener is known as a DZUS Standard Line fasteneravailable from DZUS Fastener Co., Inc., West Islip, N.Y. It can beappreciated that both tension member 3 and compression member 5inherently allow rotation of their respective first and second ends withrespect to each other. Relative rotation occurs when first connectingone end of the FTS and then subsequently connecting the other end. It isunderstood that other types of connecting means such as a pin andclevis, a threaded stud and nut, etc. are within the scope of theinvention. Likewise, connector means 7 may comprise the male or thefemale portions of any connector known to one skilled in the art thatwill support both tensile and compressive loads.

FIG. 2A shows an enlarged view of a portion of the FTS. As seen in FIG.2A, compression member 5, which is shown to be a helical spring, havinga portion 18 wherein the coils of the spring are spaced from each otherto provide a specific amount of compliance and preload to compressionmember 5. The coils of expanded portion 18 abut against portion 29 ofconnector means 7 which is operatively connected to tension member 3. Itcan be appreciated that the spacing and/or strength of the coils of thecompression member 5 will control the snap action of the FTS as shown inFIG. 10A.

FIGS. 3B and 3C illustrate a compression member 5 fabricated from aplurality of incompressible members 6, as discussed earlier. The membersmay be planar and/or fitted to each other, as seen in FIG. 3B.

FIG. 4 illustrates an alternate embodiment similar to FIGS. 2A-B whereinthe compression and compliance of compression member 5 by tensionmember3 may be controlled and/or eliminated. In FIG. 4, the outside ofconnection means 7 is threaded, and compression nut 31 is provided toselectively eliminate the compliance and compress the coils ofcompression member 5 to reduce and/or eliminate any spacing between thecoils of compressive member 5. With the embodiment illustrated in FIG.4, the rigidity of an assembled structure of FTS can be increasedsubsequent to assembly by tightening compression nut 31 associated witheach FTS. It is understood that other mechanical means besides threadedstud 19 and compression nut 31 are within the scope of the invention,such as a sliding sleeve, a spacer sleeve and other mechanicalmechanisms that will compress the coils of compression member 5 and arewell known to a person having ordinary skill in the art.

As shown in FIGS. 5A, 5B, 6A and 6B, coupler 58 is designed to takeadvantage of high volume injection molding. The body of coupler 33 canbe made in a single piece substantially identical to that shown in 5Bpiece or can be made by combining two identical pieces 32 and 32 asshown in FIGS. 5A and 5B. Each piece 32 has a perimeter 49 and an axis43 therethrough and is symmetrical about said axis. Surrounding theperimeter 49 of coupler half 32 are portions of at least one cavity 37.By manufacturing the coupler 33 in two pieces as shown, a simple twopiece, inexpensive straight pull, injection mold can be used. Theassembly of the pieces 32 (halves) of coupler 33 together in mirrorimage fashion, is facilitated by alignment pins 34 and detents 36complementary to each other and asymmetrically located about axis 43.Other features may be used for alignment prior to bonding the two halvestogether such as the perimeter 49 of coupler halves 32 themselves.Coupler 33 incorporates pins 39 for engaging slot 61 in the connectionmeans.

As previously described connection means 7 is inserted into cavity 37 byaligning slot 51 and pin 39. After insertion complete connection isobtained by rotating connection means 7, 90 degrees, until pin 39 clicksinto position 55. The end portion 23 of connection means 7 can bottomout on cavity 37 providing additional support when the FTS is subjectedto compressive loads. When the FTS is subjected to tensile loads,support is provided by pin 39 and wall 53. Bending loads areaccommodated by the wall of the cavity 37 and the end portion 23 of theconnection means 7 and rib section 59.

The coupler may be used in either a two dimensional configuration asshown in FIG. 5B or mated together with another identical coupler toform a three dimensional coupler as shown in FIG. 6B. Firm retention ofthe two couplers together is provided by bumps 38 being forced intogrooves 40. As can be appreciated coupler 33 may contain any number orsides not just 8 sides as shown. In fact couplers containing 3 or 6sides are especially useful for creating geodesic domes etc. Due to theflexibility of struts 1 any combination of different sided couplers maybe used during construction since the struts are flexible and notrestricted to fabrication using only combinations of right triangles asin other construction toys.

As shown in FIGS. 6A and 6B, coupler slot 35 is a location means for thetwo couplers 33 relative to each other. This beveled slot 41, extendingfrom the perimeter 49 and being symmetrical about the axis 43 providesalignment during mating of the two couplers and can also be used to mateto other, differing coupler pieces. The depth of this slot should be atleast to the centerline of the coupler and preferably past thecenterline so that other segments may be inserted into this slot andtheir centerline coincide with that of the coupler. This groove depthpassing beyond the centerline of the part is in contrast to the prior anteachings of Willis U.S. Pat. No. 3,564,758 which states that the slotthickness should be less than half the length of the corner radius. Thethickness of the coupler shown in FIG. 5B is substantially greater thanthe slot width. This feature is in contrast to the prior an teachings ofNelson U.S. Pat. No. 2,633,662 and Glickman U.S. Pat. No. 5,199,919 thatteach that the part thickness is less than the slot width. With thegreater part thickness of the instant invention the assembled couplersassume a spherical appearance rather than the snow-flake appearance ofthe prior art. In addition, after mating the two piece composite coupleris able to withstand loads in all directions including off center loadsand bending loads. The two couplers can be demated however, by applyingsufficient force to overcome the detent action of bumps 38 and grooves40. Each piece 32 is provided with bumps 38 and grooves 40 which arecomplementary to each other and symmetrical bout axis 43. The coupler isable to withstand the significant loads encountered when a structure iscollapsed and subsequently is allowed to re-erect itself. This abilityto be collapsed and re-erect itself is possible due to the unique natureof the FTS combined with coupler 33.

Prior art hub type couplers are not designed to accommodate all of thevarious loads encountered by the FTS when it is subjected to loadsand/or collapse. For example Glickman in U.S. Pat. No. 5,199,919discloses a hub type connector that can support small compression ortension loads but no bending loads. In fact, mating and demating of thestruts and hubs is accomplished by bending the strut relative to thehub. Earlier type hub and strut toys such as Benjamin, U.S. Pat. No.2,709,318, Pajeau, U.S. Pat. No. 1,113,371 and Ferris, U.S. Pat. No.1,843,115 disclose hubs with holes for attaching struts by forcing astrut into a under size hole. Removal is accomplished by pulling on thestrut thus pulling it out of the hole. This type of attachment method,since it cannot accommodate supporting tensile loads would not besuitable for the FTS which experiences compressive, tensile and bendingloads during assembly and during any subsequent external loading orcollapse. The hub strut connection system shown in FIG. 9 is able toaccommodate these various loads without demating and thus provide arugged structure that can even be collapsed without demating andcompromising the structural integrity of the structure.

Other rugged connection systems are disclosed in the prior art such asthe nut and bolt arrangement disclosed by Gugliotta in U.S. Pat. No.3,882,650 but this system is obviously cumbersome and time consuming andwould never be tolerated by a child in a building set. The connectionsystem disclosed in Ono U.S. Pat. No. 3,864,049 can support tension andcompression and is quickly connected, but by virtue of its design inorder to support tension, it cannot be demated once mated. Since the FTScan be bent in order to insert it into a coupler hole, the buildingsequence used during construction of a structure is not important. Inother words the builder will not have to remove a piece of the structurein order to fit another because the FTS pieces are bendable and inaddition the two end pieces rotate independent of each other thusallowing mating of one end without interfering with the other. In orderto allow maximum flexibility of a FTS structure, ball and socket jointscould be used in order to provide the smallest joint possible. Acollapsible structure is disclosed in Adams U.S. Pat. No. 4,958,474.This system uses rigid struts with flexible joints to allow collapsewhere as the FTS system uses flexible struts to provide flexibility. Inaddition the system of Adams does not possess an energy storage systemactivated during collapse, thus cannot self-erect due to storage ofenergy.

It can be appreciated that the coupler 33 can have a plurality ofopenings 37 to accommodate the connection of struts in all threedimensions. It can be appreciated that the top surface 35 of the member33 can be contoured and provided with further openings (not shown) toaccommodate struts at angles to surface 45 other than perpendicular.

As shown in FIGS. 7 and 8, connector means 7 provides for transmittingtensile, compressive and bending loads to be applied to the couplers andthe entire structure. To facilitate easy and fast connection to thecouplers the end pieces require only a 90 degree rotation (quarter turn)to completely engage and lock in place. This locking action is providedby the action of the coupler tooth 39, extending to engage a connector,being rotated past ramp 57 and into final position 55. The action oftooth 39 sliding though ramp section 57 proves a tactile and audibleclick confirming to the user that the end piece has been fully mated. Asis shown in FIGS. 7 and 8 tooth 39 is wider than slot 61. As theconnector means 7 is rotated and tooth 39 is forced into ramp section 57and circumferential rib 59 is deflected and then snaps back into itsoriginal position after tooth 39 completes its travel into its finalposition at position 55. It is understood that rib 59 need not extendaround the complete circumference of connection means 7. The stiffnessof rib 59 determines the amount of force required to fully mateconnector means 7 into coupler 33. Connector means 7 has been speciallydesigned to incorporate locking collar section 9, entry section 51,spring rib section 59, ramp section 57 and grasping section 25 all intoa single injection moldable piece. In addition the design of theexternal portions is such that they can be molded in a simple two piecemold that opens in a straight pull without elaborate multi- axis slides.This is very advantageous in order to keep the mold tooling costs downto a reasonable level. In order to incorporate entry portion 51 and rampportion 57 in a design that is moldable in a two piece mold, thatretracts in a single direction, these features must not contain anyunder-cuts that would prevent the removal of the connection means aftermolding. This is accomplished by aligning the walls of slot 51 parallelto parting line 63 and second wall 65 perpendicular to parting line 63.The walls of slot 51 are perpendicular to slot 61 including ramp 57 andrib 59. As can be appreciated the angle these features have with respectto parting line 63 need not be exactly parallel or perpendicular toparting line 63 but they must not create undercuts, i.e., portions ofthe end piece that are narrower at the bottom than the top.

A strut mated to two couplers is shown in FIG. 8. FIG. 9 illustrates astructure fabricated from a plurality of flexible tie struts 1 andcouplers 33. It can be appreciated that each FTS, even after assembly,can be flexed, as shown in FIG. 1, and the entire assembly compressed.

FIGS. 10A and 10B illustrate the force versus deflection curves for aflexible tie strut and spring loaded as a cantilever and in column.These FIGURES were discussed at length to illustrate the advantages ofthe FTS over a simple spring.

FIG. 11A illustrates a FTS compression member with 11 pounds of preloadbent into a 0.500 inch radius. FIG. 11B illustrates a spring with 11pounds of preload bent into a 0.500 inch radius.

FIG. 12 illustrates a wheel assembly with wheel 71 in FIGS. 12A and 12Bwhich utilizes an axle-like member 67 which includes both male andfemale connection means shown at 7 and 75, respectively. Femaleconnection means 75 comprises cavity 37 and tooth 39, similar to thatused in coupler 33. Male connection means 7 is a quarter-turn connectorsimilar to that used for the FTS.

Modifications and variations of the present invention will be apparentto those having ordinary skill in the an having read the aboveteachings, and the present invention is thus limited only by the spiritand scope of the following claims.

What is claimed is:
 1. A coupler comprising a body of two identicalpieces, each piece having a generally planar mating surface and having aperimeter and having an axis therethrough and being generallysymmetrical about said axis, each piece having a portion of at least onepartial cavity in the perimeter thereof and in the generally planarmating surface, said pieces being connected together by contact of saidmating surfaces in mirror image and coplanar fashion joining saidportions to form said body having a complete cavity in the peripherythereof to form a two-dimensional connector.
 2. A coupler as in claim 1wherein each said piece has alignment projections and detents which areasymmetrical about said axis, said projections and detents beingcomplementary to each other to provide alignment for assembly of eachpiece to each other.
 3. A coupler as in claim 1 having a beveled slot ineach piece extending from the perimeter of each piece and beingsymmetrical about said axis, said beveled slots having beveled surfacesproviding alignment of said body to an identical body of identicalpieces to form a three-dimensional coupler, the beveled surfacescontacting each other to provide continuous alignment and stability whenformed as a three-dimensional coupler.
 4. A coupler as in claim 1wherein each said piece has bumps and grooves which are symmetricalabout said axis, said bumps and grooves being complementary to eachother to provide for retention of said body to another body.
 5. Acoupler as in claim 1 wherein said cavities have at least one toothextending into said cavity to engage a connector means of a tie strut tobe mated to said coupler.
 6. A self erecting system comprising aflexible tie strut for supporting both compressive and tensile forceshaving a first connector means attached to the first ends of saidtension member and said compression member and a second connector meansattached to said second ends of said tension member and compressionmember to connect said flexible tie strut to objects to be connected andhaving a coupler having a body of two-identical pieces, each piecehaving a perimeter and having an axis therethrough and being generallysymmetrical about said axis, each piece having a portion of at least onecavity in the perimeter thereof, said pieces being connected together inmirror image fashion to form said body having cavities in the peripherythereof to form a two-dimensional connector.
 7. A system as in claim 6wherein said connector means includes a flexible tie strut wherein saidconnector means includes at least a portion of a circumferentialresilient rib, said rib being deflected upon mating of said strut.
 8. Aself erecting system comprising a flexible tie strut for supporting bothcompressive and tensile forces having a first connector means attachedto the first ends of said tension member and said compression member anda second connector means attached to said second ends of said tensionmember and compression member to connect said flexible tie strut toobjects to be connected and having a coupler having a body oftwo-identical pieces, each piece having a perimeter and having a couplerhaving a perimeter and at least one cavity, in said perimeter, saidcavity having at least one tooth extending into said cavity to engage aconnector means of a tie strut to be mated to said coupler.
 9. A systemas in claim 8 wherein said connector means includes a flexible tie strutwherein said connector means includes at least a portion of acircumferential resilient rib, said rib being deflected upon mating ofsaid strut.
 10. A wheel assembly comprising:at least one wheel having arotational axis and having an opening therethrough concentric with saidaxis; and an axle-like member permanently mounted within said opening,said axle-like member having connector means integral with each endthereof, said connector means being a quarter-turn connector at one endand a cavity that is complimentary in dimension to said quarter turnconnector having at least one tooth at the other end thereof.